Publications (81)191.86 Total impact

Conference Paper: The SM and NLO Multileg Working Group: Summary Report
[Show abstract] [Hide abstract]
ABSTRACT: After years of waiting, and after six Les Houches workshops, the era of LHC running is finally upon us, albeit at a lower initial centerofmass energy than originally planned. Thus, there has been a great sense of anticipation from both the experimental and theoretical communities. The last two years, in particular, have seen great productivity in the area of multiparton calculations at leading order (LO), nexttoleading order (NLO) and nexttonexttoleading order (NNLO), and this productivity is reflected in the proceedings of the NLM group. Both religions, Feynmanians and Unitarians, as well as agnostic experimenters, were wellrepresented in both the discussions at Les Houches, and in the contributions to the writeup. Nexttoleading order (NLO) is the first order at which the normalization, and in some cases the shape, of perturbative cross sections can be considered reliable. This can be especially true when probing extreme kinematic regions, as for example with boosted Higgs searches considered in several of the contributions to this writeup. A full understanding for both standard model and beyond the standard model physics at the LHC requires the development of fast, reliable programs for the calculation of multiparton final states at NLO. There have been many advances in the development of NLO techniques, standardization and automation for such processes and this is reflected in the contributions to the first section of this writeup. Many calculations have previously been performed with the aid of seminumerical techniques. Such techniques, although retaining the desired accuracy, lead to codes which are slow to run. Advances in the calculation of compact analytic expressions for Higgs + 2 jets have resulted in the development of much faster codes, which extend the phenomenology that can be conducted, as well as making the code available to the public for the first time. A prioritized list of NLO cross sections was assembled at Les Houches in 2005 and added to in 2007. This list includes cross sections which are experimentally important, and which are theoretically feasible (if difficult) to calculate. Basically all 23 cross sections of interest have been calculated, with the frontier now extending to 2 {yields} 4 calculations. Often these calculations exist only as private codes. Since 2007, two additional calculations have been completed: t{bar t}b{bar b} and W+3 jets, reflecting the advance of the NLO technology to 2 {yields} 4 processes. In addition, the cross section for b{bar b}b{bar b} has been calculated for the q{bar q} initial state with the gg initial state calculation in progress. Final states of such complexity usually lead to multiscale problems, and the correct choice of scales to use can be problematic not only at LO, but also at NLO. The size of the higher order corrections and of the residual scale dependence at NLOcan depend strongly on whether the considered cross section is inclusive, or whether a jet veto cut has been applied. Depending on the process, dramatically different behavior can be observed upon the application of a jet veto. There is a tradeoff between suppressing the NLO cross section and increasing the perturbative uncertainty, with application of a jet veto sometimes destroying the cancellation between infrared logs of real and virtual origin, and sometimes just suppressing large (and very scalesensitive) treelevel contributions. So far, there is no general rule predicting the type of behavior to be expected, but this is an important matter for further investigation. From the experimental side, an addition to the above wishlist that will be crucial is the determination of the accuracy to which each of the calculations needs to be known. This is clearly related to the experimental accuracy at which the cross sections can be measured at the LHC, and can determine, for example, for what processes it may be necessary to calculate electoweak corrections, in addition to the higher order QCD corrections. On the theoretical side, it would also be interesting to categorize the impact of a jet veto on the size and stability of each of the NLO cross sections. The technology does exist to carry out a calculation for W/Z production at NNLO (QCD) and at NLO (EW). This process was placed on the wishlist in 2007 and it is unfortunate that the combined calculation has not yet been carried out, as this precision benchmark will be very useful and important at the LHC.  [Show abstract] [Hide abstract]
ABSTRACT: The production of one hard jet in association with missing transverse energy is a major LHC search channel motivated by many scenarios for physics beyond the Standard Model. In scenarios with a weakly interacting dark matter candidate, like supersymmetry, it arises from the associated production of a quark partner with the dark matter agent. We present the nexttoleading order cross section calculation as the first application of the fully automized MadGolem package. We find moderate corrections to the production rate with a strongly reduced theory uncertainty.  [Show abstract] [Hide abstract]
ABSTRACT: This report summarizes the activities of the SM and NLO Multileg Working Group of the Workshop "Physics at TeV Colliders", Les Houches, France 826 June, 2009. 
Article: Nexttoleading order QCD corrections to p p → b b ¯ b b ¯ + X at the LHC: The quark induced case
[Show abstract] [Hide abstract]
ABSTRACT: The production of two b¯b pairs is a prominent background for Higgs and New Physics searches in various extensions of the Standard Model. We present here the nexttoleading order QCD corrections to the quark induced subprocess using the GOLEM approach for the virtual corrections. We show that our result considerably improves the prediction and conclude that the inclusion of nexttoleading order effects is indispensable for reliable studies of b¯bb¯b observables in hadronic collisions.  [Show abstract] [Hide abstract]
ABSTRACT: In this talk we review the GOLEM approach to oneloop calculations and present an automated implementation of this technique. This method is based on Feynman diagrams and an advanced reduction of oneloop tensor integrals which avoids numerical instabilities. We have extended our oneloop integral library golem95 with an automated oneloop matrix element generator to compute the virtual corrections of the process $q\bar{q}\to b\bar{b}b\bar{b}$. The implementation of the virtual matrix element has been interfaced with treelevel Monte Carlo programs to provide the full result for the above process. Comment: 8 pages, 1 figure, contribution to the proceedings of the 9th International Symposium on Radiative Corrections (RADCOR 2009), October 2530 2009, Ascona, Switzerland  [Show abstract] [Hide abstract]
ABSTRACT: A fully differential calculation of the nexttoleading order QCD corrections to the production of Zboson pairs in association with a hard jet at the Tevatron and LHC is presented. This process is an important background for Higgs particle and new physics searches at hadron colliders. We find sizable corrections for cross sections and differential distributions, particularly at the LHC. Residual scale uncertainties are typically at the 10% level and can be further reduced by applying a veto against the emission of a second hard jet. Our results confirm that NLO corrections do not simply rescale LO predictions.  [Show abstract] [Hide abstract]
ABSTRACT: In this talk we discuss recent progress concerning precise predictions for hadron colliders. We show results of two applications of tensor reduction using GOLEM methods: the nexttoleading order (NLO) corrections to $pp \to ZZ+$jet as an important background for Higgs particle and new physics searches at hadron colliders, and the NLO corrections to graviton plus jet hadroproduction, which is an important channel for graviton searches at the Tevatron and the LHC.  [Show abstract] [Hide abstract]
ABSTRACT: Many highly developed Monte Carlo tools for the evaluation of cross sections based on tree matrix elements exist and are used by experimental collaborations in high energy physics. As the evaluation of oneloop matrix elements has recently been undergoing enormous progress, the combination of oneloop matrix elements with existing Monte Carlo tools is on the horizon. This would lead to phenomenological predictions at the nexttoleading order level. This note summarises the discussion of the nexttoleading order multileg (NLM) working group on this issue which has been taking place during the workshop on Physics at TeV Colliders at Les Houches, France, in June 2009. The result is a proposal for a standard interface between Monte Carlo tools and oneloop matrix element programs.Dedicated to the memory of, and in tribute to, Thomas Binoth, who led the effort to develop this proposal for Les Houches 2009. Thomas led the discussions, set up the subgroups, collected the contributions, and wrote and edited this paper. He made a promise that the paper would be on the arXiv the first week of January, and we are faithfully fulfilling his promise. In his honour, we would like to call this the Binoth Les Houches Accord. 
Article: golem95: A numerical program to calculate oneloop tensor integrals with up to six external legs
[Show abstract] [Hide abstract]
ABSTRACT: We present a program for the numerical evaluation of form factors entering the calculation of oneloop amplitudes with up to six external legs. The program is written in Fortran95 and performs the reduction to a certain set of basis integrals numerically, using a formalism where inverse Gram determinants can be avoided. It can be used to calculate oneloop amplitudes with massless internal particles in a fast and numerically stable way.  [Show abstract] [Hide abstract]
ABSTRACT: This report summarizes the activities of the SM and NLO Multileg Working Group of the Workshop "Physics at TeV Colliders", Les Houches, France 826 June, 2009.  [Show abstract] [Hide abstract]
ABSTRACT: In this talk I report on recent developments and results relevant for LHC phenomenology at nexttoleading order QCD. Feynman diagrammatic and unitarity based methods have both seen considerable improvements and new ideas recently. Current approaches point towards automated evaluation of oneloop multiparticle amplitudes. Many results for notoriously difficult processes are under construction by several groups and, given the enormous recent progress, it can be concluded that LHC phenomenology at full nexttoleading order level will become the standard approximation soon. Comment: 25 pages latex, 20 eps figures included. To appear in the proceedings of the 12th International Workshop on Advanced Computing and Analysis Techniques in Physics Research, ACAT 2008, Erice, Sicily, November 37, 2008. Replaced with revised version, minor changes, references added  [Show abstract] [Hide abstract]
ABSTRACT: A calculation of the loopinduced gluonfusion process gg > Z(photon)Z(photon) > l antil l' antil' is presented, which provides an important background for Higgs boson searches in the H > ZZ channel at the LHC. We find that the photon contribution is important for Higgs masses below the Zpair threshold and that the gginduced process yields a correction of about 15% relative to the NLO QCD prediction for the q antiqinduced process when only a M(l antil), M(l' antil') > 5 GeV cut is applied.  [Show abstract] [Hide abstract]
ABSTRACT: In this talk we present recent nexttoleading order results relevant for LHC phenomenology obtained with the GOLEM method. After reviewing the status of this Feynman diagrammatic approach for multileg oneloop calculations we discuss three applications: the loopinduced process gg→Z∗Z∗ and the virtual corrections to the five and six point processes qq→ZZg and . We demonstrate that our method leads to representations of such amplitudes which allow for efficient phase space integration. In this context we propose a reweighting technique of the leading order unweighted events by local Kfactors.  [Show abstract] [Hide abstract]
ABSTRACT: We present a calculation of the NLO QCD corrections for the production of three vector bosons at the LHC, namely Z Z Z, W+ W Z, W+ Z Z, and W+ W W+ production. The virtual corrections are computed using the recently proposed method of reduction at the integrand level (OPP reduction). Concerning the contributions coming from real emission we used the dipole subtraction to treat the soft and collinear divergences. We find that the QCD corrections for these electroweak processes are in the range between 70 and 100 percent. As such they have to be considered in experimental studies of triple vector boson production at the LHC.  [Show abstract] [Hide abstract]
ABSTRACT: This report summarizes the activities of the NLM working group of the Workshop "Physics at TeV Colliders", Les Houches, France, 1129 June, 2007. 
Conference Paper: Higgs Working Group Summary Report
[Show abstract] [Hide abstract]
ABSTRACT: Report of the Working Group on Higgs Bosons for the Workshop, ``Physics at TeV Colliders'', Les Houches, France, 1129 June, 2007.  [Show abstract] [Hide abstract]
ABSTRACT: In this talk we discuss recent progress concerning precise predictions for the LHC. We give a status report of three applications of our method to deal with multileg oneloop amplitudes: The interference term of Higgs production by gluon and weak boson fusion to order O(alpha^2 alpha_s^3) and the nexttoleading order corrections to the two processes pp > ZZ jet and u ubar > d dbar s sbar. The latter is a subprocess of the four jet cross section at the LHC. 

Conference Paper: Gluon induced QCD corrections to pp → ZZ → l ̄l l' ̄l'
 [Show abstract] [Hide abstract]
ABSTRACT: We calculate the order O(α2α3 s) interference effect between the gluon fusion and weak boson fusion processes allowed at the oneloop level in Higgs boson plus 2 jet production at the LHC. The corresponding oneloop amplitudes, which have not been considered in the literature so far, are evaluated analytically using dimensional regularisation and the necessary master integrals with massive propagators are reported. It is discussed in detail how various mechanisms conspire to make this contribution numerically negligible for experimental studies at the LHC.
Publication Stats
3k  Citations  
191.86  Total Impact Points  
Top Journals
Institutions

20012011

The University of Edinburgh
 School of Physics and Astronomy
Edinburgh, Scotland, United Kingdom


2006

Scottish Universities Physics Alliance
Glasgow, Scotland, United Kingdom


20042005

University of Wuerzburg
 Department of Theoretical and Astrophysics
Würzburg, Bavaria, Germany


19961997

University of Freiburg
Freiburg, BadenWürttemberg, Germany
